华北地区四种岩石在高压下的破坏特征

利用我国第一台1GPa高压三轴容器进行了岩石破坏实验.所用的样品为济南辉长岩、昌平花岗岩、房山大理岩和周口店石灰岩.得到的主要结果是:(1)在相应于地壳的压力范围内辉长岩和花岗岩仍然发生脆性破坏, 其强度和韧度随围压增加而增加, 破坏角也随围压增加而增大, 破坏前发生体积膨胀现象并出现声发射活动增加的前兆;(2)大理岩和石灰岩样品在0.1——0.8GPa的围压范围内发生鼓状变形, 不形成明显的主断层面, 样品承载能力随变形增加而增加, 出现应变硬化现象.在变形过程中声发射活动水平极低。这些实验标志着我国岩石力学三轴实验的围压水平有所提高其结果对震源物理的研究具有参考价值.      

1600 K和20 GP温压条件下的顽火辉石电导率

在温度750～1600 K和压力10～20 GPa条件下,借助于Kawai-5000多面顶砧高温高压设备,就位测量了(Mg_0.9Fe_0.1) SiO₃ 顽火辉石的电导率.实验结果显示,顽火辉石的电导率在高温区以小极化子机制为主,在低温区以质子导电为主,因为实验后的样品中有一定的水含量.另外,X射线衍射实验表明压力（20 GPa）诱发了顽火辉石向林伍德石的相变,这是我们首次在顽火辉石的电导率实验中观测到林伍德石含水相变,而且含水林伍德石的电导率与已有的实验结果相当一致.     

大麻坪橄榄石冲击波实验研究与高压态物态方程参数的确定

利用冲击波进行的动高压实验对研究超高压下的物质性质也是十分有效的.本文报告了对大麻坪采集的橄榄石进行压力在10~45GPa范围的冲击波动高压实验结果.结合前人等温冷压实验结果,确定了实验过程的温度,对于冲击波实验压力从10GPa变化到30GPa时,温度在摄氏几十度到摄氏800多度之间.测量了岩石超高压下密度变化,在3.627~4.009g·cm~(-3)之间.通过回收实验和确定的温度,表明小于30GPa压力实验条件下,没有发生相变过程.同时也确定了状态方程的参数.最后,指出了实验结果在上地幔地球内部物质运动过程的含义,即冷板块中的亚临界橄榄岩可以存在地幔转换带中.     

加载、加热路径上橄榄石的相变及其对相变动力学参数计算的影响

本文研究了橄榄石原位相变实验中加载、加热路径上的相变及其对确定相变动力学参数的影响.利用文献［1］所给出的退火后先加温后加压,且相对低温条件下实验结果确定出的Ni₂SiO₄橄榄石相变动力学参数,计算了加载、加热路径上所发生的相变对确定成核率、长大率及相变体积分数的影响.结果表明,退火后先加压后加温,且相对高温条件下的实验数据受到加热路径上成核的影响.根据这样的实验数据得到的成核率会明显高于实际温压条件下的成核率.尤其是当多数实验都是高温实验时,根据这些成核率数据所确定的成核率参数会严重偏离其真值,从而严重影响对俯冲带颗粒粒度及俯冲带流变结构的计算.尽管目前有很多关于Mg₂SiO₄橄榄石长大率的实验数据,也有通过对挤碰物理图像的分析对(Mg_0.89Fe_0.11)₂SiO₄橄榄石成核率的估算,但只有文献［2］通过退火后先加压后加温的原位实验得到了Mg₂SiO₄橄榄石的相变成核率,且属于高温实验.根据本文的研究结果,我们认为亟需补充退火后先加温后加压或相对低温的实验数据以得到正确的地幔橄榄石成核率参数.     

地幔转换带底部橄榄石和辉石高压相变实验研究：对660km地震不连续面结构的启示

橄榄石和辉石以及它们的高压相是地幔转换带主要矿物,系统研究橄榄石和辉石在转换带底部温度和压力条件下相变的差异是认识660km地震不连续面位置和形态的关键．本文使用多面砧压机开展了橄榄石和顽火辉石在压力为21．3～24．4GPa,温度为1600℃的相变实验研究．地幔转换带底部,橄榄石和顽火辉石相变主要的差异在于钙钛矿出现的压力不同．在橄榄石体系中,后尖晶石相分解发生在23．8GPa,与660km不连续面具有很好的对应关系;而在顽火辉石体系中,钙钛矿出现的压力小于23GPa．研究结果表明,橄榄石后尖晶石相变与辉石中钙钛矿的出现之间有约0．5—1GPa压力差．因此,在受大洋俯冲带影响地区（例如中国东部）,辉石体系中发生的秋本石（钛铁矿）．钙钛矿的相变能够合理解释660km地震不连续面向上的起伏或分裂．     

西藏南部蛇绿岩套电导率研究

大地电磁(MT)资料显示,青藏高原地壳及地幔中普遍存在着高导层.作为大陆造山带中古洋盆岩石圈残片,蛇绿岩套的电导率测量可为了解古洋盆地区地壳及地幔的电性结构提供极其有用的信息.本研究中,我们在压力为1 GPa或3 GPa下,用交流阻抗谱法测量了采自西藏南部地区的蚀变辉长岩、玄武岩、角闪橄榄岩及方辉橄榄岩四个样品的阻抗谱,并进一步得出样品的电导率,不同样品电导率与温度之间的关系满足Arrhenius关系式.在实验温度范围内,蛇绿岩套电导率的对数logσ位于-6.0~-0.5 S/m之间,且随着温度的增高,不同样品电导率增大约4~5.5个量级.样品在未脱水的情况下,低温段的活化焓变化范围在0.4~0.6 eV之间,高温段的活化焓变化范围为1.7~2.6 eV之间.同时,我们研究了样品中结构水含量及铁含量对实验电导率的影响,验证了样品电导率与铁含量之间呈正比关系.当对样品结构水含量进行归一化后,相同温度下各样品的电导率随铁含量的增加而增大,而对样品铁含量归一化后,相同温度下各样品的电导率随样品中水含量的增加而增大.将实验电导率与藏南地区大地电磁结果进行了对比,发现本研究中各样品高温段实验电导率结果均落在大地电磁结果范围内.     

新疆东准噶尔花岗岩类岩石高温高压弹性波速度及其对地壳结构的约束

应用超声波反射-透射法,在最高压力为1.0 GPa（室温）,最高温度为700℃（1.0 GPa）的条件下对新疆东准噶尔地区的卡拉麦里花岗岩带和野马泉岩体的典型花岗岩类岩石（碱长花岗岩、碱性花岗岩、花岗闪长岩、二长花岗岩和石英闪长岩）的纵波速度（V_P）和横波速度（V_S）进行了测量.结果显示,在常温、压力0.4~1.0 GPa条件下,东准噶尔地区花岗岩类岩石的V_P和V_S均随压力呈线性增加,说明在这个压力段岩石中的微裂隙已基本闭合.室温、1.0 GPa时花岗岩类岩石的V_P是5.79~6.84 km·s^-1,V_S是3.26~3.85 km·s^-1.依据压力与V_P及压力与V_S的线性关系,拟合得到常温常压下花岗岩类岩石的纵波和横波压力系数分别是0.1568~0.4078 km/（s·GPa）和0.0722~0.3271 km/（s·GPa）,V_P0和V_S0分别是5.62~6.47 km·s^-1和3.15~3.75 km·s^-1.恒压1.0 GPa、室温到700℃条件下,花岗岩类岩石的V_P和V_S均随温度的升高呈线性降低,温度系数分别为（-3.41~-4.96）×10^-4 km/（s·℃）和（-0.88~-3.22）×10^-4 km/（s·℃）.利用实验获得的花岗岩类岩石的V_P0、V_S0及温度系数和压力系数,结合东准噶尔地区的地热资料,建立了V_P和V_S随深度变化的剖面.将获得的V_P和V_S-深度剖面与该区地球物理探测结果对比,发现东准噶尔地区的碱长花岗岩、碱性花岗岩、二长花岗岩和部分花岗闪长岩的V_P和V_S与该区上地壳速度吻合很好,同时这几种岩石的平均泊松比也与上地壳泊松比一致,因此我们认为这几种类型的岩石是该区上地壳的重要组成部分.另外,石英闪长岩的V_P和V_S均符合中地壳的速度,可能为中地壳中的一种岩石.     

岩石超高压状态参数的实验研究

岩石的超高压状态参数对研究地球动力学问题和岩石爆破工程问题具有十分重要的意义.本实验应用平面波炸药透镜驱动飞板撞击靶板产生超高压冲击波,并用探针测量冲击波在岩石试件中的传播速度和粒子速度,再由 Rankine-Hugoniot 方程得到岩石的密度与压力之间的关系.所研究的岩石为石灰岩和花岗岩.实验的最高压力超过70GPa.得到两种岩石的超高压状态方程是:石灰岩————=3.22+0.016p;花岗岩————=3.20+0.024p.其中的单位为 g/cm3,p 的单位为 GPa.      

活塞-圆桶式固体介质高温高压实验容器的压力标定方法

固体介质压力标定一般分为2方面。其一是轴压标定,最有效的方法是轴压活塞反复前进和后退,根据活塞循环来获得摩擦力的大小,其中有2个关键环节:1)活塞和样品接触点的确定;2)动摩擦力的确定。其二是围压标定,最有效的方法是利用矿物相变,适用于固体压机压力标定的相变有:石英-柯石英相变、钠长石-硬玉+石英相变,其适合温压范围分别为:500~1200℃、2.5~3.2GPa,600~1200℃、1.6~3.2GPa。我们对2GPa固体介质高温高压实验设备进行了轴压标定,在不同温度、围压、活塞速率等条件下进行了实验,结果表明:围压、温度、活塞运动速率等因素都对动摩擦力有不同程度的影响。因此,轴压标定应该针对不同的实验条件分别进行     

非线性有效压力计算

根据Robin关于有效压力的定义,结合Bernabé推测的孔隙压p_p和围压p_c图中的渗透率等值线变化形态,提出了一种新的非线性渗透率有效压力计算方法.用新方法和Bernabé切线有效压力计算方法对以往和本次实验的12块低渗岩芯的实验数据进行了处理分析,结果表明新方法和Bernabé方法计算得到的有效压力在p_p和p_c图中的渗透率等值线为直线时才相等.当等值线为曲线时,二者计算得到的有效压力不一样.新方法计算出的测试点的有效压力与渗透率的关系表现出更好的一一对应关系.为了进一步验证文章计算有效压力方法的有效性,用指数和乘幂两种函数分别拟合二种有效压力计算方法得到的有效压力与渗透率之间的关系.拟合结果表明,新方法得到的有效压力与渗透率的拟合效果优于用Bernabé方法计算得到的有效压力与渗透率拟合效果.     

Shock-induced devolatilization of calcite

The amounts of CO₂ and CO evolved upon shock compression and decompression of calcite to 18 GPa (180 kbar) have been determined using a new gas phase shock recovery technique and gas source mass spectrometry. The data demonstrate that from ～0.03 to 0.3 mole percent of calcite is devolatilized at shock pressures significantly lower than those predicted (30 GPa) for the onset of volatilization by continuum thermodynamic theory and are in qualitative agreement with release adiabat data for calcite and aragonite. Carbon and oxygen isotope ratios in the shock-released CO₂ are the same as those in the unshocked (hydrothermal) calcite, demonstrating that the CO₂ comes from the calcite rather than other potential sources.     

The effect of ferromagnetism on the equation of state of Fe3C studied by first-principles calculations

First-principles calculations have been used to determine the equation of state of Fe₃C in both its low-pressure magnetically ordered and high-pressure non-magnetically ordered states; at 0 K the ferromagnetic transition was found to occur at about 60 GPa. In the high pressure, non-magnetically ordered regime at 0 K the material may be described by a Birch-Murnaghan third-order equation of state with V₀=8.968(7) ų per atom, K₀=316.62(2) GPa and K′=4.30(2). At atmospheric pressure the ferromagnetic phase transition in Fe₃C occurs at ∼483 K; preliminary measurements of the thermal expansion by powder neutron diffraction show that this transition produces a large effect on thermoelastic properties. The volumetric thermal expansion coefficient in the paramagnetic phase was found to be 4.34×10⁻⁵ K⁻¹ at T∼550 K. By applying a thermal expansion correction to the calculated equation of state at 0 K, predicted values for the density and adiabatic incompressibility of this material at core pressures and temperatures were obtained. These results appear to be sufficiently different from seismological data so as to preclude Fe₃C as the major inner core-forming phase.     

Viscosity of peridotite liquid up to 13 GPa: Implications for magma ocean viscosities

The viscosity of synthetic peridotite liquid has been investigated at high pressures using in-situ falling sphere viscometry by combining a multi-anvil technique with synchrotron radiation. We used a newly designed capsule containing a small recessed reservoir outside of the hot spot of the heater, in which a viscosity marker sphere is embedded in a forsterite + enstatite mixture having a higher solidus temperature than the peridotite. This experimental setup prevents spheres from falling before a stable temperature above the liquidus is established and thus avoids difficulties in evaluating viscosities from velocities of spheres falling through a partially molten sample.

Experiments have been performed between 2.8 and 13 GPa at temperatures ranging from 2043 to 2523 K. Measured viscosities range from 0.019 (± 0.004) to 0.13 (± 0.02) Pa s. At constant temperature, viscosity increases with increasing pressure up to  8.5 GPa but then decreases between  8.5 and 13 GPa. The change in the pressure dependence of viscosity is likely associated with structural changes of the liquid that occur upon compression. By combining our results with recently published 0.1 MPa peridotite liquid viscosities [D.B. Dingwell, C. Courtial, D. Giordano, A. Nichols, Viscosity of peridotite liquid, Earth Planet. Sci. Lett. 226 (2004) 127–138.], the experimental data can be described by a non-Arrhenian, empirical Vogel-Fulcher-Tamman equation, which has been modified by adding a term to account for the observed pressure dependence of viscosity. This equation reproduces measured viscosities to within 0.08 log₁₀-units on average. We use this model to calculate viscosities of a peridotitic magma ocean along a liquid adiabat to a depth of  400 km and discuss possible effects on viscosity at greater pressures and temperatures than experimentally investigated.     

Simultaneous volume measurements of post-perovskite and perovskite in MgSiO3 and their thermal equations of state

Simultaneous volume measurements of MgSiO₃ post-perovskite (PPv) and perovskite (Pv) were performed in a diamond anvil cell (DAC) combined with synchrotron X-rays. An externally-heated DAC was used in addition to a laser-heated DAC for the volume measurement experiment at high temperatures. The volume data were collected in the stability field of post-perovskite from 115 to 130 GPa. The temperature generated in the externally-heated and the laser-heated DACs for the volume measurement were up to 832 and 2330 K, respectively. Using two different but complementary heating techniques, we collected the data at a wide temperature range from 300 to 2330 K. The obtained P-V-T data for PPv and Pv were fitted to a third-ordered Birch-Murnaghan equation of state (EOS). For a precise comparison of the volume between the two phases, the EOSs were constructed based on the same pressure scale of MgO. The simultaneous volume measurements and the volumes calculated from the determined EOSs demonstrate that the volume difference between PPv and Pv of about 1.5% is almost constant with increasing temperature to 4000 K at the transition. At the base of the mantle, this density difference corresponds to a temperature anomaly of 1300 K without the phase transition due to the very small thermal expansivity of minerals, which has a significant effect on mantle dynamics. The thermal expansivity contrast between the top and the bottom of the mantle is a factor of 3.6. From a mantle convection study, this value suggests that huge and hot plumes are formed at the core–mantle boundary.     

Thermodynamic properties of calcium ferrite-type MgAl2O4: A first principles study

The diamond anvil cell experiments have revealed that the calcium ferrite(CF)-type aluminous phase is probably an important component of subducted mid-oceanic ridge basalt(MORB) in the lower mantle. In this study, we have performed first principles lattice dynamics calculations for the Mg Al_2O_4 end-member of the aluminous phase based on density functional perturbation theory using two functionals within the local density approximation(LDA) and generalized gradient approximation(GGA) for bracketing the calculated properties at their lower and upper limits, respectively. A simple empirical pressure correction at zero temperature has been applied to both LDA and GGA. The results of room-temperature equation of state(EOS) and zero-pressure thermal expansion calculated by GGA with pressure correction have shown the best agreement with available experimental data. The high-pressure and temperature thermodynamic properties have been obtained using the GGA with correction method. The pressure-volume relations are fitted with a third-order high-temperature Birch-Murnaghan EOS. The isobaric heat capacity, the coefficient of thermal expansion and isothermal bulk modulus are fitted with polynomials and their coefficients are reported in the range of 0–40 GPa and 300–2000 K. The density profile of MORB estimated using the computational thermo-elastic constants supports the hypothesis that the subducted oceanic slabs could gain enough downwelling forces into the lower mantle.     

Elasticity of (Mg0.83,Fe0.17)O ferropericlase at high pressure: ultrasonic measurements in conjunction with X-radiation techniques

The elasticity of ferropericlase with a potential mantle composition of (Mg_0.83,Fe_0.17)O is determined using ultrasonic interferometry in conjunction with in situ X-radiation techniques (X-ray diffraction and X-radiography) in a DIA-type cubic anvil high-pressure apparatus to pressures of 9 GPa (NaCl pressure scale) at room temperature. In this study, we demonstrate that it is possible to directly monitor the specimen length using an X-ray image technique and show that these lengths are consistent with those derived from X-ray diffraction data when no plastic deformation of the specimen occurs during the experiment. By combining the ultrasonic and X-ray diffraction data, the adiabatic elastic bulk (K_S) and shear (G) moduli and specimen volume can be measured simultaneously. This enables pressure scale-free measurements of the equation of state of the specimen using a parameterization such as the Birch-Murnaghan equation of state. The elastic moduli determined for (Mg_0.83,Fe_0.17)O are K_S0=165.5(12) GPa, G₀=112.4(4) GPa, and their pressure derivatives are K_S0′=4.17(20) and G₀′=1.89(6). If these results are compared with those for MgO, they demonstrate that K_S0 and K_S0′ are insensitive to the addition of 17 mol% FeO, but G₀ and G₀′ are reduced by 14% and 24%, respectively. We calculate that the P and S wave velocities of a perovskite plus ferropericlase phase assemblage with a pyrolite composition at the top of the lower mantle (660 km depth) are lowered by 0.8 and 2.3%, respectively, when compared with those calculated using the elastic properties of end-member MgO. Consequently, the magnitudes of the calculated wave velocity jumps across the 660 km discontinuity are reduced by about 11% for P wave and 20% for S wave, if this discontinuity is considered as a phase transformation boundary only (ringwoodite→perovskite+ferropericlase).     

Effect of high-pressures on the electrical resistivity of natural zeolites from Deccan Trap, Maharashtra, India

We report here the electrical resistivity measurements on two natural zeolites–natrolite and scolecite (from the Killari borehole, Maharashtra, India) as a function of pressure up to 8 GPa at room temperature. High-pressure electrical resistivity studies on hydrous alumino-silicate minerals are very helpful in understanding the role of water in deep crustal conductivities obtained from geophysical models. The results obtained by magneto-telluric (MT) soundings and direct current resistivity surveys, along with the laboratory data on the electrical resistivity of minerals and rocks at high-pressure–temperature are used to determine the electrical conductivity distribution in continental lithosphere. The electrical resistivity of natural natrolite decreases continuously from 2.9 × 10⁹ Ω cm at ambient condition to 7.64 × 10² Ω cm at 8 GPa, at room temperature. There is no pressure-induced first order structural phase transitions in natrolite, when it is compressed in non-penetrating pressure transmitting medium up to 8 GPa. On the other hand scolecite exhibits a pressure-induced transition, with a discontinuous decrease of the electrical resistivity from 2.6 × 10⁶ to 4.79 × 10⁵ Ω cm at 4.2 to 4.3 GPa. The observed phase transition in scolecite is found to be irreversible. Vibrational spectroscopic and X-ray diffraction studies confirm the amorphous nature of the high-pressure phase. The results of the present high-pressure studies on scolecite are in good agreement with the high-pressure Raman spectroscopic data on scolecite. The thermo gravimetric studies on the pressure-quenched samples show that the samples underwent a pressure-induced partial dehydration. Such a pressure-induced partial dehydration, which has been observed in natural scolecite could explain the presence of high conductive layers in the earth's deep-crust.     

Thermal equation of state of majorite with MORB composition

In situ synchrotron X-ray diffraction experiments were conducted using the SPEED-1500 multi-anvil press at SPring-8 on majoritic garnet synthesized from natural mid-ocean ridge basalt (MORB), whose chemical composition is close to the average of oceanic crust, at 19 GPa and 2200 K. Pressure-volume-temperature data were collected using a newly developed high-pressure cell assembly to 21 GPa and 1273 K. Data were fit to the high-temperature Birch-Murnaghan equation of state, with fixed values for the ambient cell volume (V₀ = 1574.14(4) Å³) and the pressure derivative of the isothermal bulk modulus (K^′T = 4). This yielded an isothermal bulk modulus of K_T0 = 173(1) GPa, a temperature derivative of the bulk modulus (∂K_T/∂T)_P = −0.022(5) GPa K⁻¹, and a volumetric coefficient of thermal expansivity α = a + bT with values of a = 2.0(3) × 10⁻⁵ K⁻¹ and b = 1.0(5) × 10⁻⁸ K⁻². The derived thermoelastic parameters are very similar to those of pyrope. The density of subducted oceanic crust compared to pyrolitic mantle at the conditions in Earth's transition zone (410-660 km depth) was calculated using these results and previously reported thermoelastic parameters for MORB and pyrolite mineral assembledges. These calculations show that oceanic crust is denser than pyrolitic mantle throughout the mantle transition zone along a normal geotherm, and the density difference is insensitive to temperature at the pressures in lower part of the transition zone.     

Laboratory measurements of ‘porosity‐free’ intrinsic Vp and Vs in an olivine gabbro of the Oman ophiolite: Implication for interpretation of the seismic structure of lower oceanic crust

In order to determine ‘porosity‐free’ intrinsic ultrasonic compressional (Vp) and shear wave (Vs) velocities and Vp/Vs of an olivine gabbro from the Oman ophiolite, we developed a new experimental system using a piston‐cylinder type high‐pressure apparatus. The new system allowed us to measure velocities at pressures ranging from 0.20 to 1.00 GPa and at temperatures up to 300°C for Vp and 400°C for Vs. At room temperature, the Vp and Vp/Vs increase rapidly with pressure up to 0.40 GPa, while between 0.45 and 1.00 GPa the increase is more gradual. The change in increasing rate is attributed to closure of porosity at pressures above 0.45 GPa. Based on the linear regression of data obtained at higher pressures (0.45–1.00 GPa) and extrapolation to the lower pressures, combined with temperature derivatives of velocities of the sample measured at 1.00 GPa, we determined the intrinsic Vp and Vs of the sample as a function of pressure (P, in GPa) and temperature (T, in °C). The intrinsic velocities can be expressed as Vp (km/s) = 7.004 + 0.096 × P ? 0.00015 × T, and Vs (km/s) = 3.827 + 0.007 × P ? 0.00008 × T. We evaluated the intrinsic Vp and Vs of the olivine gabbro at oceanic crustal conditions and compared them with a velocity depth‐profile of the borehole seismic observatory WP‐2 area in the northwestern Pacific Basin. Although the intrinsic Vp (～7.0 km/s) and Vs (～3.8 km/s) for the olivine gabbro studied are comparable to those of seismic layer 3 in the WP‐2 area, the estimated vertical gradients of intrinsic velocities are significantly smaller than those reported from layer 3. These results suggest that velocity profiles of layer 3 in the WP‐2 area may reflect the presence of a minor porosity in lower oceanic crust, which closes with increasing depth and/or continuous changes in mineralogy of layer 3 rocks.     

Melting of forsterite Mg2SiO4 up to 15 GPa

The melting curve of forsterite has been studied by static experiment up to a pressure of 15 GPa. Forsterite melts congruently at least up to 12.7 GPa. The congruent melting temperature is expressed by the Kraut-Kennedy equation in the following form: T_m(K)=2163 (1+3.0(V₀ ? V)/V₀), where the volume change with pressure was calculated by the Birch-Managhan equation of state with the isothermal bulk modulus K₀ = 125.4 GPa and its pressure derivative K′ = 5.33. The triple point of forsterite-β-Mg₂SiO₄-liquid will be located at about 2600°C and 20 GPa, assuming that congruent melting persists up to the limit of the stability field of forsterite. The extrapolation of the previous melting data on enstatite and periclase indicates that the eutectic composition of the forsterite-enstatite system should shift toward the forsterite component with increasing pressure, and there is a possibility of incongruent melting of forsterite into periclase and liquid at higher pressure, although no evidence on incongruent melting has been obtained in the present experiment.